Search results for "conical"
showing 9 items of 109 documents
An Efficient Damping Technique for the Unstable Hysteretic Rotor Whirl by Proper Suspension Systems
2009
This paper shows as the destabilising influence of the shaft hysteresis on the supercritical rotor whirl can be efficiently counterbalanced by external dissipative sources. After calculating the steady whirling paths of the rotor and the bearing due to unbalance, the stability is checked by the Routh-Hurwitz procedure, investigating the influence of the stiffness anisotropy of the supports. A fairly interesting result is that the instability phenomena can be conveniently prevented by different suspension stiffness in the horizontal and vertical planes.
The role of the low-lying dark np* states in the photophysics of pyrazine: a quantum dynamics study
2014
The excited state dynamics of pyrazine has attracted considerable attention in the last three decades. It has long been recognized that after UV excitation, the dynamics of the molecule is impacted by strong non-adiabatic effects due to the existence of a conical intersection between the B2u(ππ*) and B3u(nπ*) electronic states. However, a recent study based on trajectory surface hopping dynamics simulations suggested the participation of the Au(nπ*) and B2g(nπ*) low-lying dark electronic states in the ultrafast radiationless decay of the molecule after excitation to the B2u(ππ*) state. The purpose of this work was to pursue the investigation of the role of the Au(nπ*) and B2g(nπ*) states in…
Quantum chemical study on the population of the lowest triplet state of psoralen
2007
Abstract The efficient population of the low-lying triplet ππ * state of psoralen is studied with the quantum chemical CASPT2 method. Minima, singlet–triplet crossings, conical intersections, and reaction paths on the low-lying singlet and triplet states hypersurfaces of the system have been computed together with electronic energy gaps and spin–orbit coupling terms. A mechanism is proposed, favorable in the gas phase, for efficient deactivation of the initially populated singlet excited ππ * state, starting with an intersystem crossing with an n π * triplet state and evolving via a conical intersection toward the final lowest-lying ππ * triplet state, protagonist of the reactivity of psora…
Pyrene, a Test Case for Deep-Ultraviolet Molecular Photophysics
2019
We determined the complete relaxation dynamics of pyrene in ethanol from the second bright state, employing experimental and theoretical broadband heterodyne detected transient grating and two-dimensional photon echo (2DPE) spectroscopy, using pulses with duration of 6 fs and covering a spectral range spanning from 250 to 300 nm. Multiple lifetimes are assigned to conical intersections through a cascade of electronic states, eventually leading to a rapid population of the lowest long-living excited state and subsequent slow vibrational cooling. The lineshapes in the 2DPE spectra indicate that the efficiency of the population transfer depends on the kinetic energy deposited into modes requir…
Adenine and 2-aminopurine: Paradigms of modern theoretical photochemistry
2006
Distinct photophysical behavior of nucleobase adenine and its constitutional isomer, 2-aminopurine, has been studied by using quantum chemical methods, in particular an accurate ab initio multiconfigurational second-order perturbation theory. After light irradiation, the efficient, ultrafast energy dissipation observed for nonfluorescent 9H-adenine is explained here by the nonradiative internal conversion process taking place along a barrierless reaction path from the initially populated 1 (ππ* L a ) excited state toward a low-lying conical intersection (CI) connected with the ground state. In contrast, the strong fluorescence recorded for 2-aminopurine at 4.0 eV with large decay lifetime …
Normal pressures and frictional tractions on shallow conical hopper walls after concentric filling: Predictions and experiments
2013
Author's version of an article in the journal: Chemical Engineering Science. Also available from the publisher at: http://dx.doi.org/10.1016/j.ces.2012.11.028 A silo with a shallow hopper is designed to achieve the required silo capacity when the headroom available is limited, provided that the issue of segregation of stored particulate solids is not a problem. Several analytical models have been proposed to try to predict the design loads for such shallow silo hoppers to guarantee their structural integrity. In this study, a novel finite element analysis has been conducted to explore the development of pressures and tractions on the wall of a full scale shallow hopper when it is filled wit…
Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field
2014
International audience; Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recentl…
Two examples related to conical energies
2022
In a recent article we introduced and studied conical energies. We used them to prove three results: a characterization of rectifiable measures, a characterization of sets with big pieces of Lipschitz graphs, and a sufficient condition for boundedness of nice singular integral operators. In this note we give two examples related to sharpness of these results. One of them is due to Joyce and M\"{o}rters, the other is new and could be of independent interest as an example of a relatively ugly set containing big pieces of Lipschitz graphs.
LA SCALA DI MOMO AI MUSEI VATICANI. Curve coniche gobbe e superfici rigate da esse generate.
2014
This study is part of a more vast research that aims to examine in depth the geometrical-spatial origin of skew curves belonging to conical surfaces of revolution: conical spiral and conical helix. The study begins with an investigation concerning the geometrical tracing, and the spatial origin of both the skew curves and the ruled surfaces they generate, carrying out a comparison of the different formal characteristics through a number of algorithms that control the reference properties, written within the renown Rhinoceros plug-in, Grasshopper. Then follows an in-depth analysis of an admirable example of architecture dating back to the first thirty years of the past century and made by th…